The present invention generally relates to a semiconductor device and a method for fabricating the same. More particularly, the present invention relates to a semiconductor device including a capacitor device having a capacitive insulating film of insulating metal oxide film such as a ferroelectric film or a high dielectric film (i.e., a film made of a material having a high dielectric constant) and to a method for fabricating the same.
In recent years, as various electronic units such as microcomputers operating at an even higher speed and with even lower power consumption have been developed, the performance of consumer-use electronic units have also been further enhanced. Correspondingly, the sizes of semiconductor devices used for these units have also been rapidly reduced drastically.
As semiconductor devices have been miniaturized, unwanted radiation, i.e., electromagnetic wave noise generated from electronic units, has become a serious problem. Technology for incorporating a large-capacity capacitor device, including a ferroelectric film or a high dielectric film as a capacitive insulating film, into a semiconductor integrated circuit is now the object of much attention as a means for reducing the unwanted radiation.
On the other hand, since a very highly integrated dynamic RAM is now provided, researches have been widely carried out on technology for using a high dielectric film as a capacitive insulating film, instead of a silicon oxide film or a silicon nitride film, which has been conventionally used.
Furthermore, in order to put into practical use a non-volatile RAM operating with a low voltage and enabling high-speed write and read operations, researches and developments have also been vigorously carried out on a ferroelectric film having spontaneous polarization properties. A ferroelectric memory using a ferroelectric film as a capacitive insulating film takes advantage of a phenomenon that the amount of charge flowing into/out of a data line of a ferroelectric memory differs depending upon whether or not the spontaneous polarization of the ferroelectric film is inverted.
In all of these types of semiconductor devices mentioned above, it is an urgent task to develop technology for realizing very high integration for a capacitor device without deteriorating the characteristics thereof.
Hereinafter, a conventional semiconductor device will be described with reference to FIG. 13.
FIG. 13 illustrates a cross-sectional structure of a conventional semiconductor device. As shown in FIG. 13, a lower electrode 2 made of a first platinum film, a capacitive insulating film 3 made of a ferroelectric film and an upper electrode 4 made of a second platinum film are formed in this order on a semiconductor substrate 1 made of silicon. The lower electrode 2, the capacitive insulating film 3 and the upper electrode 4 constitute a capacitor device. An interlevel insulating film 5 made of a silicon oxide film, a silicon nitride film or the like is deposited to cover the entire surface of the semiconductor substrate 1 as well as the capacitor device. A lower-electrode contact hole 6 and an upper-electrode contact hole 7 are formed through the interlevel insulating film 5. Metal interconnections 8, each consisting of a titanium film 8a, a first titanium nitride film 8b, an aluminum film 8c and a second titanium nitride film 8d, are formed to cover the interlevel insulating film 5 as well as the inner surfaces of the lower-electrode contact hole 6 and the upper-electrode contact hole 7.
Hereinafter, a method for fabricating the conventional semiconductor device will be described with reference to FIGS. 14(a) through 14(e).
First, as shown in FIG. 14(a), the first platinum film 2A, the ferroelectric film 3A and the second platinum film 4A are sequentially stacked over the entire surface of the semi-conductor substrate 1. Thereafter, as shown in FIG. 14(b), the second platinum film 4A is selectively etched, thereby forming the upper electrode 4. Then, in order to recover and stabilize the crystal structure of the ferroelectric film 3A, the ferroelectric film 3A is subjected to a heat treatment within oxygen ambient.
Next, as shown in FIG. 14(c), the ferroelectric film 3A and the first platinum film 2A are selectively etched, thereby forming the capacitive insulating film 3 out of the ferroelectric film 3A and the lower electrode 2 out of the first platinum film 2A. Then, in order to recover and stabilize the crystal structure of the ferroelectric film constituting the capacitive insulating film 3, the capacitive insulating film 3 is subjected to a heat treatment within oxygen ambient.
Subsequently, as shown in FIG. 14(d), the interlevel insulating film 5 made of a silicon oxide film or a silicon nitride film is deposited over the entire surface of the semi-conductor substrate 1. And the lower-electrode contact hole 6 and the upper-electrode contact hole 7 are formed through the interlevel insulating film 5. Then, in order to recover and stabilize the crystal structure of the ferroelectric film constituting the capacitive insulating film 3, the capacitive insulating film 3 is subjected to a heat treatment within oxygen ambient.
In order to prevent the lower electrode 2 or the upper electrode 4 from being oxidized as a result of the reaction between the lower electrode 2 or the upper electrode 4 with the capacitive insulating film 3 during the heat treatment conducted to recover and stabilize the crystal structure of the ferroelectric film, the lower and the upper electrodes 2, 4 are made of platinum, which is hard to react with the ferroelectric film 3A constituting the capacitive insulating film 3 during the heat treatment and exhibits anti-oxidation properties even at a high temperature.
Then, as shown in FIG. 14(e), the titanium film 8a, the first titanium nitride film 8b, the aluminum film 8c and the second titanium nitride film 8d are sequentially deposited to cover the entire surface of the semiconductor substrate 1 as well as the inner surfaces of the lower-electrode contact hole 6 and the upper-electrode contact hole 7, thereby forming the metal interconnections 8, each consisting of the titanium film 8a, the first titanium nitride film 8b, the aluminum film 8c and the second titanium nitride film 8d. The titanium film 8a functions as an adhesive film for improving the adhesion between the aluminum film 8c and the platinum film constituting the upper electrode 4. The first titanium nitride film 8b functions as a barrier film for preventing aluminum in the aluminum film 8c from diffusing into the capacitive insulating film 3. The second titanium nitride film 8d functions as an anti-reflection film while an upper interlevel insulating film deposited over the metal interconnections 8 is etched.
Next, in order to further improve the adhesion between the titanium film 8a constituting the metal interconnections 8 and the interlevel insulating film 5, the metal interconnections 8 are subjected to a heat treatment.
However, during the heat treatment conducted to stabilize the crystal structure of the ferroelectric film, the platinum film constituting the upper electrode comes to have column like crystal structure. Thus, during the heat treatment conducted to improve the adhesion between the metal interconnections and the interlevel insulating film, the titanium atoms in the titanium film constituting the metal interconnections adversely pass through the grain boundary of the column like crystals of the platinum film constituting the upper electrode so as to diffuse into the capacitive insulating film. As a result, since the composition of the ferroelectric film or the high dielectric film constituting the capacitive insulating film is varied, the electrical characteristics of the capacitor device are disadvantageously deteriorated.
It is not only when the upper electrode is made of platinum but also when the upper electrode is made of iridium, ruthenium, rhodium, palladium or the like that the upper electrode ordinarily has a column like crystal structure. Thus, in the latter case, the titanium atoms in the titanium film constituting the metal interconnections also adversely pass through the grain boundary of the column like crystals constituting the upper electrode so as to diffuse into the capacitive insulating film.
In view of the foregoing, the object of the present invention is to prevent titanium atoms in a titanium film from passing through the grain boundary of metal crystals composing the upper electrode of a capacitor device and diffusing into a capacitive insulating film during a heat treatment conducted on metal interconnections, which are formed on the capacitor device and include the titanium film.
In order to accomplish the object, the semiconductor device according to the present invention includes: a substrate; a capacitor device, which is formed on the substrate and includes a capacitive lower electrode, a capacitive insulating film made of an insulating metal oxide film and a capacitive upper electrode; an interlevel insulating film, which is formed on the capacitor device and has an opening reaching the capacitive upper electrode; a metal interconnection, which is formed on the interlevel insulating film so as to be electrically connected to the capacitive upper electrode through the opening and includes a titanium film; and an anti-diffusion film, which is formed between the capacitive upper electrode and the metal interconnection, has conductivity and prevents titanium atoms composing the titanium film of the metal interconnection from passing through the capacitive upper electrode and diffusing into the capacitive insulating film.
In the semiconductor device of the present invention, an anti-diffusion film for preventing titanium atoms composing the titanium film of the metal interconnection from passing through the capacitive upper electrode and diffusing into the capacitive insulating film is formed between the capacitive upper electrode and the metal interconnection. Thus, during the heat treatment on the metal interconnection, the titanium atoms in the titanium film do not pass through the grain boundary of metal crystals composing the capacitive upper electrode and do not diffuse into the capacitive insulating film. Accordingly, a semiconductor device including a highly reliable capacitor device can be formed.
In the semiconductor device of the present invention, the anti-diffusion film is preferably a metal nitride film or metal oxide film having conductivity.
In such an embodiment, since the conductive metal nitride film or metal oxide film has no grain boundary and has a dense structure, the film can prevent the passage of titanium atoms with certainty. In particular, if the anti-diffusion film is a conductive metal oxide film, the conductivity of the film is not damaged even when a heat treatment is conducted within oxygen ambient in order to recover the crystal structure of the ferroelectric film constituting the capacitive insulating film. This is because the metal oxide film has conductivity in the state of an oxide.
In the semiconductor device of the present invention, if the capacitive insulating film is a ferroelectric film, a highly reliable nonvolatile memory can be obtained. On the other hand, if the capacitive insulating film is a high dielectric film, a highly reliable dynamic memory can be obtained.
In the semiconductor device of the present invention, the titanium film is preferably an adhesive layer, formed as a lowermost layer of the metal interconnection, for improving adhesion between the metal interconnection and the upper electrode, and the anti-diffusion film is preferably a titanium nitride film.
In such an embodiment, since the titanium film is an adhesive layer, the adhesion between the metal interconnection and the upper electrode can be improved. In addition, if the anti-diffusion film is a titanium nitride film, then no by-product is formed during the deposition of the anti-diffusion film. Moreover, even if titanium in the titanium film diffuses toward the anti-diffusion film over a certain distance, the nature of the anti-diffusion film is not changed and the characteristics of the capacitor device are stabilized.
In the semiconductor device of the present invention, the capacitive upper electrode preferably has a crystal structure including a grain boundary.
In such an embodiment, although the titanium atoms are more likely to pass through the capacitive upper electrode, the titanium atoms do not diffuse into the capacitive insulating film because the atoms are prevented by the anti-diffusion film from reaching the capacitive upper electrode.
A first method for fabricating a semiconductor device according to the present invention includes the steps of: forming a capacitor device, including a capacitive lower electrode, a capacitive insulating film made of an insulating metal oxide film and a capacitive upper electrode, on a substrate; forming an interlevel insulating film, having a contact hole reaching the capacitive upper electrode, on the capacitor device; depositing a conductive film, preventing the passage of titanium atoms therethrough, so as to cover the entire surface of the interlevel insulating film as well as the contact hole; patterning the conductive film such that at least a part of the conductive film located inside the contact hole is left, thereby forming an anti-diffusion film out of the conductive film; and forming, on the interlevel insulating film, a metal interconnection including a titanium film such that the metal interconnection is electrically connected to the capacitive upper electrode via the anti-diffusion film.
In the first method for fabricating a semiconductor device, a conductive film, preventing the passage of titanium atoms, is deposited over an interlevel insulating film formed on the capacitor device and including a contact hole. Then, the conductive film is patterned, thereby leaving the part of the conductive film located inside the contact hole. Thus, the anti-diffusion film for preventing the titanium atoms from passing through the capacitive upper electrode and diffusing into the capacitive insulating film can be formed between the upper electrode of the capacitor device and the metal inter-connection with certainty.
A second method for fabricating a semiconductor device according to the present invention, includes the steps of: forming a capacitor device, including a capacitive lower electrode, a capacitive insulating film made of an insulating metal oxide film and a capacitive upper electrode, on a substrate; forming an interlevel insulating film, having a contact hole reaching the capacitive upper electrode, on the capacitor device; forming, on the interlevel insulating film, a resist pattern having an opening at a site corresponding to the contact hole; depositing a conductive film, preventing the passage of titanium atoms therethrough, so as to cover the entire surface of the resist pattern; lifting off the conductive film together with the resist pattern such that a part of the conductive film located inside the contact hole is left, thereby forming an anti-diffusion film out of the conductive film; and forming, on the interlevel insulating film, a metal interconnection including a titanium film such that the metal interconnection is electrically connected to the capacitive upper electrode via the anti-diffusion film.
In the second method for fabricating a semiconductor device, a resist pattern having an opening at a site corresponding to a contact hole is formed on the interlevel insulating film formed on the capacitor device and including the contact hole, and a conductive film, preventing the passage of titanium atoms therethrough, is deposited thereon. Thus, the anti-diffusion film for preventing the titanium atoms from passing through the capacitive upper electrode and diffusing into the capacitive insulating film can be formed between the upper electrode of the capacitor device and the metal interconnection with certainty.
A third method for fabricating a semiconductor device according to the present invention includes the steps of: sequentially stacking a first metal film, an insulating metal oxide film, a second metal film and a conductive film, preventing the passage of titanium atoms therethrough, on a substrate; patterning the second metal film and the conductive film by using the same etching mask, thereby forming a capacitive upper electrode out of the second metal film and an anti-diffusion film out of the conductive film; patterning the insulating metal oxide film to form a capacitive insulating film and patterning the first metal film to form a capacitive lower electrode; forming an interlevel insulating film, having a contact hole reaching the capacitive upper electrode, over a capacitor device constituted by the capacitive lower electrode, the capacitive insulating film and the capacitive upper electrode; and forming, on the interlevel insulating film, a metal interconnection including a titanium film such that the metal interconnection is electrically connected to the capacitive upper electrode via the anti-diffusion film.
In the third method for fabricating a semiconductor device, among the sequentially stacked first metal film, insulating metal oxide film, second metal film and conductive film preventing the passage of titanium atoms therethrough, the second metal film and the conductive film are patterned first, thereby forming a capacitive upper electrode and an anti-diffusion film. Then, a metal interconnection including a titanium film is formed over the interlevel insulating film having a contact hole. Thus, the anti-diffusion film for preventing the titanium atoms from passing through the capacitive upper electrode and diffusing into the capacitive insulating film can be formed between the upper electrode of the capacitor device and the metal interconnection with certainty.
A fourth method for fabricating a semiconductor device according to the present invention includes the steps of: forming a capacitive lower electrode and a capacitive insulating film made of an insulating metal oxide film on a substrate; depositing an interlevel insulating film so as to cover the substrate as well as the capacitive insulating film; forming a resist pattern over the interlevel insulating film, the resist pattern having an opening over a region where a capacitive upper electrode is to be formed; etching the interlevel insulating film by using the resist pattern as a mask, thereby forming an upper electrode forming opening through the interlevel insulating film; sequentially depositing a metal film and a conductive film preventing the passage of titanium atoms therethrough so as to cover the entire surface of the resist pattern as well as the upper electrode forming opening; lifting off the metal film and the conductive film together with the resist pattern such that part of the metal film and part of the conductive film, which are located in the upper electrode forming opening, are left, thereby forming the capacitive upper electrode out of the metal film and an anti-diffusion film out of the conductive film; and forming, on the interlevel insulating film, a metal interconnection including a titanium film such that the metal interconnection is electrically connected to the capacitive upper electrode via the anti-diffusion film.
In the fourth method for fabricating a semiconductor device, the interlevel insulating film is etched by using, as a mask, a resist pattern including an opening over the region where the capacitive upper electrode is to be formed, thereby forming an upper electrode forming opening through the interlevel insulating film. Then, a metal film and a conductive film preventing the passage of titanium atoms therethrough are deposited, and a metal interconnection including a titanium film is formed thereon. Thus, the anti-diffusion film for preventing the titanium atoms from passing through the capacitive upper electrode and diffusing into the capacitive insulating film can be formed between the upper electrode of the capacitor device and the metal interconnection with certainty.
Therefore, in accordance with the first to fourth methods for fabricating a semiconductor device, the semiconductor device of the present invention can be fabricated with certainty.
In the first to fourth methods for fabricating a semiconductor device, the conductive film is preferably a metal nitride film or metal oxide film having conductivity.
In the first to fourth methods for fabricating a semiconductor device, the capacitive insulating film is preferably a ferroelectric film or a high dielectric film.
In the first to fourth methods for fabricating a semiconductor device, the titanium film is preferably an adhesive layer, formed as a lowermost layer of the metal interconnection, for improving adhesion between the metal interconnection and the capacitive upper electrode, and the anti-diffusion film is preferably a titanium nitride film.
In the first to fourth methods for fabricating a semiconductor device, the capacitive upper electrode preferably has a crystal structure including a grain boundary.